U.S. patent number 6,927,421 [Application Number 10/279,959] was granted by the patent office on 2005-08-09 for heat sink material.
This patent grant is currently assigned to NGK Insulators, Ltd.. Invention is credited to Shuhei Ishikawa, Tsutomu Mitsui, Nobuaki Nakayama, Ken Suzuki, Hiroyuki Takeuchi, Seiji Yasui.
United States Patent |
6,927,421 |
Ishikawa , et al. |
August 9, 2005 |
**Please see images for:
( Certificate of Correction ) ** |
Heat sink material
Abstract
A mass of graphite is placed into a case, and the case is put
into a furnace (step S301). The space in the furnace is heated to
produce a porous sintered body of graphite (step S302). Thereafter,
the case with the porous sintered body contained therein is removed
from the furnace, and put into a cavity in a press (step S303).
Then, a molten mass of a metal is poured into the case (step S304),
and a punch is inserted into the cavity to press the molten metal
into the porous sintered body in the case (step S305).
Inventors: |
Ishikawa; Shuhei (Handa,
JP), Mitsui; Tsutomu (Chita-Gun, JP),
Takeuchi; Hiroyuki (Handa, JP), Yasui; Seiji
(Handa, JP), Suzuki; Ken (Handa, JP),
Nakayama; Nobuaki (Tokai, JP) |
Assignee: |
NGK Insulators, Ltd. (Nagoya,
JP)
|
Family
ID: |
26624128 |
Appl.
No.: |
10/279,959 |
Filed: |
October 24, 2002 |
Foreign Application Priority Data
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Sep 18, 2002 [JP] |
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2002-272133 |
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Current U.S.
Class: |
257/76;
257/E23.109; 257/E23.11; 428/408; 428/446; 428/469; 428/698 |
Current CPC
Class: |
C22C
1/1036 (20130101); C22C 9/10 (20130101); C22C
12/00 (20130101); H01L 21/4871 (20130101); H01L
23/373 (20130101); H01L 23/3736 (20130101); C22C
2001/1021 (20130101); C22C 2001/1052 (20130101); C22C
2001/1057 (20130101); H01L 2924/0002 (20130101); H01L
2924/0002 (20130101); H01L 2924/00 (20130101); Y10T
428/30 (20150115) |
Current International
Class: |
C22C
12/00 (20060101); C22C 9/10 (20060101); H01L
032/12 () |
Field of
Search: |
;257/76
;428/408,469,446,698 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0 859 410 |
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Aug 1998 |
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EP |
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0 987 231 |
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EP |
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1 000 915 |
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May 2000 |
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EP |
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1 143 512 |
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Oct 2001 |
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EP |
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1 160 860 |
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Dec 2001 |
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EP |
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1 284 250 |
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Feb 2003 |
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EP |
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1 291 913 |
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Mar 2003 |
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EP |
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53-064474 |
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Jun 1978 |
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JP |
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59-228742 |
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Dec 1984 |
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JP |
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62-207832 |
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Sep 1987 |
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JP |
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8-279569 |
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Oct 1996 |
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JP |
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11-140560 |
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May 1999 |
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JP |
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2000-203973 |
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Jul 2000 |
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JP |
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2001-007625 |
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Jan 2001 |
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JP |
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2001-058255 |
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Mar 2001 |
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JP |
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Other References
US. Appl. No. 09/913,353, filed Aug. 13, 2001, Ishikawa et
al..
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Primary Examiner: Turner; Archene
Attorney, Agent or Firm: Burr & Brown
Claims
What is claimed is:
1. A heat sink material comprising carbon or graphite and a metal,
said metal selected from the group consisting of Bi, Sb, Ga, and
graphite cast iron, or an alloy containing said metal, and wherein
said metal has a solidification temperature of at least 300.degree.
C.
2. A heat sink material comprising carbon or graphite and a metal,
said metal selected from the group consisting of Bi, Sb, Ga, and
graphite cast iron, or an alloy containing said metal, and wherein
said metal has a property of inhibiting segregation of the
metal.
3. A heat sink material comprising carbon or graphite and a metal,
said metal selected from the group consisting of Bi, Sb, Ga, and
graphite cast iron, or an alloy containing said metal, and wherein
said metal has a property for improving wettability of the metal
with respect to a surface of the heat sink material.
4. A heat sink material comprising carbon or graphite and a metal,
said metal selected from the group consisting of Bi, Sb, Ga, and
graphite cast iron, or an alloy containing said metal, and wherein
said metal has a property of expansion upon solidification or a
property of inhibiting a solidification shrinkage.
5. A heat sink material according to claim 4, wherein said heat
sink material has a coefficient of thermal conductivity of 300 W/mK
or higher either on the average in the directions of three
orthogonal axes or in the direction of any one of the three
orthogonal axes.
6. A heat sink material according to claim 4, wherein said carbon
or said graphite has a coefficient of thermal conductivity of 150
W/mK or higher.
7. A heat sink material according to claim 4, wherein a porous
sintered body having a network structure obtained by sintering said
carbon or said graphite is infiltrated by said metal.
8. A heat sink material according to claim 7, wherein said porous
sintered body has a porosity ranging from 10 vol. % to 50 vol. %
and an average pore diameter ranging from 0.1 .mu.m to 200
.mu.m.
9. A heat sink material according to claim 7, wherein said carbon
or said graphite has a volume ratio ranging from 50 vol. % to 90
vol. % and said metal has a volume ratio ranging from 50 vol. % to
10 vol. %.
10. A heat sink material according to claim 7, further comprising
an additive added to said carbon or said graphite for reducing a
closed porosity achieved when said carbon or said graphite is
sintered.
11. A heat sink material according to claim 10, wherein said
additive comprises SiC and/or Si.
12. A heat sink material according to claim 7, further comprising
an element added to said metal for improving the wettability at the
interface between said porous sintered body and said metal.
13. A heat sink material according to claim 12, wherein said
element comprises at least one element selected from the group
consisting of Te, Bi, Pb, Sn, Se, Li, Sb, Tl, and Cd.
14. A heat sink material according to claim 7, further comprising
an element added to said metal for improving a match and close
contact between said porous sintered body and said metal.
15. A heat sink material according to claim 7, further comprising a
carbide layer formed on a surface of said carbon or said
graphite.
16. A heat sink material according to claim 15, wherein said
carbide layer is formed on the basis of a reaction between at least
said carbon or said graphite and an additive element added
thereto.
17. A heat sink material according to claim 16, wherein said
additive element comprises at least one element selected from the
group consisting of Nb, Cr, Zr, Be, V, Mo, Al, Ta, Mn, Si, Fe, Co,
Ni, Mg, Ca, W, Ti, B, and mish metal.
18. A heat sink material according to claim 4, wherein a powder of
said carbon or said graphite and water or a binder constitutes a
mixture, and the mixture is formed into a preformed body under a
predetermined pressure or sintered into a formed body, said
preformed body or said formed body being infiltrated by said
metal.
19. A heat sink material according to claim 18, wherein said powder
of said carbon or said graphite has an average particle size
ranging from 1 .mu.m to 500 .mu.m, an average ratio of length of
each particle of said powder is 1:5 or less between a direction in
which said particle has a minimum length and a direction in which
said particle has a maximum length.
20. A heat sink material according to claim 18, wherein said carbon
or said graphite has a volume ratio ranging from 20 vol.% to 80
vol.% and said metal has a volume ratio ranging from 80 vol.% to 20
vol.%.
21. A heat sink material according to claim 18, further comprising
an element added to said metal for improving the wettability at the
interface between said porous sintered body and said metal.
22. A heat sink material according to claim 21, wherein said
additive element comprises an element selected from the group
consisting of Bi, Te, Sn, Pb, Se, Li, Sb, Tl, and Cd.
23. A heat sink material according to claim 22, wherein said
additive element comprises an additive element which forms a solid
solution with copper only at a weight ratio of at most 0.5 wt.
%.
24. A heat sink material according to claim 18, further comprising
an additive element for increasing the bonding strength between
said carbon or said graphite and said metal when said heat sink
material is molded.
25. A heat sink material according to claim 24, wherein said
additive element comprises an element selected from the group
consisting of Nb, Zr, Cr, Be, V, Mo, Al, Ta, Mn, Si, Fe, Co, Ni,
Mg, Ca, W, Ti, B, and mish metal.
26. A heat sink material according to claim 18, further comprising
an additive element added to said carbon or said graphite for
allowing the heat sink material to be reheated after said heat sink
material is molded.
27. A heat sink material according to claim 26, wherein said heat
sink material is formed on the basis of a reaction between at least
said carbon or said graphite and said additive element added
thereto.
28. A heat sink material according to claim 27, wherein said
additive element comprises an element selected from the group
consisting of Nb, Zr, Cr, Be, V, Mo, Al, Ta, Mn, Si, Fe, Co, Ni,
Mg, Ca, W, Ti, B, and mish metal.
29. A heat sink material according to claim 4, wherein a powder of
said carbon or said graphite and a powder of said metal are mixed
to obtain a mixture, and the mixture is molded under a
predetermined pressure.
30. A heat sink material according to claim 4, wherein a liquid
phase or a solid-liquid phase of said metal and a powder of said
carbon or said graphite are mixed to obtain a mixture, and said
mixture is cast into a predetermined shape.
31. A heat sink material according to claim 4, wherein a powder of
said carbon or said graphite is infiltrated by said metal.
32. A heat sink material according to claim 4, wherein a crushed
and torn material of said carbon or said graphite and a powder of
said metal are mixed to obtain a mixture, and said mixture is
molded under a predetermined pressure.
33. A heat sink material according to claim 4, further comprising a
carbide of an additive element formed on a surface of said carbon
or said graphite.
34. A heat sink material according to claim 33, wherein said
additive element comprises an element selected from the group
consisting of Nb, Zr, Cr, Be, V, Mo, Al, Ta, Mn, Si, Fe, Co, Ni,
Mg, Ca, W, Ti, B, and mish metal.
35. A heat sink material according to claim 4, wherein said heat
sink material has a residual porosity of 5% or less.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a heat sink material for a heat
sink which efficiently radiates heat generated by an IC chip, for
example.
2. Description of the Related Art
Generally, IC chips are highly susceptible to heat, and should be
designed such that their internal temperature will not exceed an
allowable maximum temperature at a junction area of the IC chips.
Semiconductor devices such as power transistors and semiconductor
rectifiers consume a large amount of electric power per operating
area, and cases (packages) and leads of such semiconductor devices
may not be effective enough to sufficiently radiate heat generated
thereby. Therefore, the internal temperature of those semiconductor
devices tends to increase to such a level that the semiconductor
devices may suffer a thermal breakdown.
The above phenomenon also occurs in IC chips incorporating CPUs. As
the clock frequency of the CPU increases, the IC chip generates
more heat while in operation. It is important to design IC chips to
incorporate a thermally designed heat radiation structure.
Thermal designs for protecting IC chips against a thermal breakdown
include device designs and mount designs which include heat sinks
having a large heat radiating area and fixed to IC chip cases
(packages).
The heat sinks are generally made of metal such as copper,
aluminum, or the like that has good thermal conductivity.
Recently, IC chips such as CPUs, memories, etc. tend to be larger
in size because of higher integration of devices and greater areas
taken up by devices, while at the same time seeking a low power
drive mode for low power consumption. IC chips of greater size are
liable to peel off position or be mechanically broken due to
increased stresses which are caused by the difference between the
coefficient of thermal expansion of the semiconductor substrate
(silicon substrate or GaAs substrate) and the coefficient of
thermal expansion of the heat sink.
Possible approaches to the prevention of the above drawbacks
include a low power drive mode for IC chips and an improvement of
heat sink materials. At present, a practical low power drive mode
for IC chips has a power supply voltage of 3.3 V rather than the
conventional TTL level (5 V).
As for heat sink materials, thermal conductivity is not the only
factor to be taken into consideration for their selection, but it
has become necessary to select heat sink materials which have a
coefficient of thermal expansion that is substantially the same as
the coefficient of thermal expansion of silicon and GaAs which the
semiconductor substrate is made of, and also have high thermal
conductivity.
Various reports have been made with respect to improved heat sink
materials. For example, proposed examples of heat sink materials
include aluminum nitride (AlN) and Cu--W (copper-tungsten). AlN is
suitable for use as a heat sink material for semiconductor devices
which use a silicon substrate because it has a coefficient of
thermal conductivity and a coefficient of thermal expansion well
balanced and particularly because its coefficient of thermal
expansion is substantially the same as the coefficient of thermal
expansion of Si.
Cu--W is suitable for use as a material of a heat sink which has a
complex shape because it is a composite material having a low
coefficient of thermal expansion provided by W and a high
coefficient of thermal conductivity provided by Cu, and it is
easily machinable.
Other examples of heat sink materials include a ceramic base
material mainly composed of SiC and containing 20 vol. % to 40 vol.
% of Cu (conventional example 1: Japanese laid-open patent
publication No. 8-279569) and a powder-sintered porous body of an
inorganic material infiltrating 5 wt. % to 30 wt. % of Cu
(conventional example 2: Japanese laid-open patent publication No.
59-228742).
The heat sink material according to the conventional example 1 is
formed by powder molding that the heat sink material is molded a
compressed powder of SiC and Cu into a heat sink. The coefficient
of thermal expansion and the coefficient of thermal conductivity of
this heat sink material are of theoretical values. Therefore, the
theoretical values cannot be balanced against the coefficient of
thermal expansion and the coefficient of thermal conductivity of
actual electronic parts.
The heat sink material according to the conventional example 2
suffers a limitation on efforts to increase the coefficient of
thermal conductivity as the ratio of Cu infiltrated into the
powder-sintered porous body is low.
The above heat sink materials are suitable for use as composite
materials having high coefficients of thermal conductivity.
However, these heat sink materials fail to achieve a desired
mechanical strength because residual pores are easily produced in
the composite materials as a sufficient pressure for infiltrating
the carbon material, such as a ceramic material for the
semiconductor base, with the metal cannot be achieved for the
reason that the mechanical strength of the carbon material is
relatively low.
The residual pores result in a reduction in the coefficient of
thermal conductivity of the composite material, an occurrence of
voids at the interface between solder and the composite material in
the step of soldering the composite material, and a reduction in
the wettability between the composite material and the solder.
In recent years, it has become possible to produce a composite
material having a high coefficient of thermal conductivity which is
achieved by a carbon material only. As a result, the need for
infiltrating metal into pores in a carbon material to produce a
composite material having a high coefficient of thermal
conductivity is decreasing. The metal serves the purpose of
reducing residual pores to increase the mechanical strength of the
heat sink material by efficiently infiltrating into the carbon
material. Other tasks that need to be accomplished quickly include
the prevention of soaking of water into residual voids that are
produced in the plating step and the prevention of voids, bulging,
and peeling which occur due to the water seepage.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a
heat sink material which is produced by infiltrating metal into
pores in a carbon material, the heat sink material containing
reduced residual pores that are produced when the metal is
infiltrated into the heat sink material and having a high
mechanical strength that is achieved by improving the wettability
between the heat sink material and a plated solder layer which
covers the surface of the heat sink material.
According to the present invention, a heat sink material comprises
carbon or an allotrope thereof and a metal, the metal comprising a
metal having a property of expansion upon solidification or a metal
having a property of inhibiting a solidification shrinkage. Since
the metal which has its volume expanded or shrunk little in the
vicinity of a solidification temperature is infiltrated into the
heat sink material, any shrinkage of the metal that occurs in a
cooling process from the solidification temperature to the room
temperature is reduced. Therefore, residual pores are prevented
from being produced in the heat sink material.
The metal comprises a metal selected from the group consisting of
Bi, Sb, Ga, and graphite cast iron, or an alloy containing the
metal. These metals have a property of expansion upon
solidification or inhibiting a solidification shrinkage.
If a metal having a low solidification temperature is selected as
the above metal, then any shrinkage of the metal that is cooled
from the solidification temperature to the room temperature is
reduced. When the heat sink material is incorporated into an actual
electronic component and soldered, the heat sink material is
reheated. Therefore, it is preferable to select a metal which is
not melted with the heat applied in the soldering process, i.e., a
metal which has a solidification temperature of 300.degree. C. or
higher.
The metal may be a metal having a low level of segregation. If a
metal having a low melting point is used, then the primary crystal
tends to be segregated and the metal may possibly be melted in a
temperature range up to 200.degree. C. as viewed from the phase
diagram.
The metal should preferably be a metal having good wettability with
respect to the heat sink material. Pores in a carbon material can
easily be infiltrated by a metal having good wettability even under
a low infiltrating pressure.
The heat sink material should preferably have a coefficient of
thermal conductivity of 300 W/mK or higher on the average in the
directions of three orthogonal axes or in the direction of any one
of the three orthogonal axes.
The carbon or the allotrope thereof, which serves as a base of the
heat sink material, should preferably have a coefficient of thermal
conductivity of 150 W/mK or higher. If the carbon or the allotrope
thereof is free of pores, then it should preferably have a
coefficient of thermal conductivity of 200 W/mK or higher, more
preferably a coefficient of thermal conductivity of 250 W/mK or
higher, or much more preferably a coefficient of thermal
conductivity of 300 W/mK or higher. By thus selecting the carbon or
the allotrope thereof, the heat sink material has a high
coefficient of thermal conductivity being independent of the type
of the metal.
The allotrope should preferably be graphite or diamond because they
have a high coefficient of thermal conductivity.
The heat sink material comprises a porous sintered body
infiltrating the metal, which the porous sintered body constructs a
network obtained by sintering the carbon or the allotrope thereof.
The porous sintered body has a porosity ranging from 10 vol. % to
50 vol. % and an average pore diameter ranging from 0.1 .mu.m to
200 .mu.m.
The carbon or the allotrope thereof has a volume ratio ranging from
50 vol. % to 90 vol. % and the metal has a volume ratio ranging
from 50 vol. % to 10 vol. %.
To produce a heat sink material having a high mechanical strength,
it is preferable to add an additive to the carbon or the allotrope
thereof for reducing a closed porosity when the carbon or the
allotrope thereof is sintered. The additive comprises SiC and/or
Si. The addition of the additive makes it possible to reduce
residual pores which are produced when the carbon or the allotrope
thereof is sintered. Particularly, if a preform made up of the
carbon or its allotrope is infiltrated by the additive, then a
infiltration ratio of the metal is increased, efficiently reducing
residual pores.
To improve the wettability at the interface between the porous
sintered body and the metal, it is preferable to add an element to
the metal, the element comprising at least one element selected
from the group consisting of Te, Bi, Pb, Sn, Se, Li, Sb, Tl, and
Cd. With the element added, the wettability between the metal and
the carbon or its allotrope is increased, allowing the porous
sintered body to be infiltrated by the metal under a low pressure,
and increasing the bonding strength at the interface. Furthermore,
the wettability between the heat sink material and a plated solder
layer on the surface of the heat sink material is increased,
reducing voids at the interface.
If a carbide layer is formed on a surface of the carbon or the
allotrope thereof, then the bonding strength between the carbon or
the allotrope and the infiltrating metal is increased by the
carbide layer, increasing the coefficient of thermal conductivity
and the mechanical strength of the heat sink material. The hardness
of the carbide layer itself contributes to the mechanical strength
of the heat Sink material. Moreover, the wettability at the
interface between the heat sink material and a plated solder layer
on the surface of the heat sink material is increased. In addition,
the metal can be infiltrated into the porous sintered body under a
low pressure, and the metal can be infiltrated into fine pores.
The carbide layer is formed on the basis of a reaction between at
least the carbon or the allotrope thereof and an additive element
added thereto. The additive element comprises at least one element
selected from the group consisting of Nb, Cr, Zr, Be, V, Mo, Al,
Ta, Mn, Si, Fe, Co, Ni, Mg, Ca, W, Ti, B, and mish metal.
The heat sink material may be not only made of the porous sintered
body and the metal, but also manufactured by mixing a powder of the
carbon or the allotrope thereof and water or a binder constitutes a
mixture, forming the mixture into a preformed body under a
predetermined pressure or sintered into a formed body, and
infiltrating the metal into the preformed body or the formed body.
Alternatively, a powder of the carbon or the allotrope thereof and
a powder of the metal may be mixed to obtain a mixture, and the
mixture may be molded under a predetermined pressure. Further
alternatively, a liquid phase or a solid-liquid phase of the metal
and a powder of the carbon or the allotrope thereof may be mixed to
obtain a mixture, and the mixture may be cast to shape. A powder of
the carbon or the allotrope thereof may be infiltrated by the
metal.
The powder of the carbon or the allotrope thereof has an average
particle size ranging from 1 .mu.m to 500 .mu.m, an average ratio
of length of each particle of said powder is 1:5 or less between a
direction in which said particle has a minimum length and a
direction in which said particle has a maximum length.
The heat sink material may be manufactured by mixing a crushed and
torn material of the carbon or the allotrope thereof and a powder
of the metal into a mixture, and forming the mixture to shape under
a predetermined pressure.
In the heat sink material thus manufactured, the carbon or the
allotrope thereof should preferably have a volume ratio ranging
from 20 vol. % to 80 vol. % and the metal should preferably have a
volume ratio ranging from 80 vol. % to 20 vol. %.
Preferably, an additive element for increasing the bonding strength
between particles of the metal should preferably be added to the
heat sink material when the heat sink material is molded. The
additive element comprises an element selected from the group
consisting of Bi, Te, Sn, Pb, Se, Li, Sb, Tl, and Cd. Preferably,
the additive element should be selected from Nb, Zr, Cr, Be, etc.
which is difficult to form a solid solution with copper. If an
additive element which forms a solid solution with copper only at a
weight ratio of at most 0.5 wt. % is added, then there is provided
a desired heat sink material whose coefficient of thermal
conductivity is not lowered.
It is preferable to add an additive element for increasing the
bonding strength between the carbon or the allotrope thereof and
the metal when the heat sink material is molded. The additive
element should preferably comprise an element selected from the
group consisting of Nb, Zr, Cr, Be, V, Mo, Al, Ta, Mn, Si, Fe, Co,
Ni, Mg, Ca, W, Ti, B, and mish metal.
An additive element may be added to the carbon or the allotrope
thereof for allowing the heat sink material to be reheated after
the heat sink material is molded. The heat sink material may be is
formed on the basis of a reaction between at least the carbon or
the allotrope thereof and the additive element added thereto. The
additive element should preferably comprise an element selected
from the group consisting of Nb, Zr, Cr, Be, V, Mo, Al, Ta, Mn, Si,
Fe, Co, Ni, Mg, Ca, W, Ti, B, and mish metal.
Preferably, a carbide of an additive element is formed on a surface
of the carbon or the allotrope thereof. The bonding strength
between the carbon or the allotrope and the infiltrating metal is
increased by the carbide, increasing the coefficient of thermal
conductivity and the mechanical strength of the heat sink material.
The hardness of the carbide itself contributes to the mechanical
strength of the heat sink material. Moreover, the metal can be
infiltrated into the porous sintered body under a low pressure, and
the metal can be infiltrated into fine pores. The additive element
should preferably comprise an element selected from the group
consisting of Nb, Zr, Cr, Be, V, Mo, Al, Ta, Mn, Si, Fe, Co, Ni,
Mg, Ca, W, Ti, B, and mish metal.
The heat sink material thus has a residual porosity of 5% or
less.
The above and other objects, features, and advantages of the
present invention will become more apparent from the following
description when taken in conjunction with the accompanying
drawings in which preferred embodiments of the present invention is
shown by way of illustrative example.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is perspective view showing a structure of a heat sink
material according to a first embodiment of the present
invention;
FIG. 2A is a front elevational view, partly in cross section, of a
high-pressure vessel used in a first manufacturing process;
FIG. 2B is a side elevational view, partly in cross section, of the
high-pressure vessel shown in FIG. 2A;
FIG. 3 is a flowchart of the first manufacturing process;
FIG. 4 is a flowchart of a first modification of the first
manufacturing process;
FIG. 5 is a flowchart of a second modification of the first
manufacturing process;
FIG. 6 is a cross-sectional view of a furnace for use in a second
manufacturing process;
FIG. 7 is a cross-sectional view of a press for use in the second
manufacturing process;
FIG. 8 is a flowchart of the second manufacturing process;
FIG. 9 is a cross-sectional view taken along line IX--IX of FIG.
1;
FIG. 10 is a graph showing densities in infiltrated regions in the
heat sink material shown in FIG. 9;
FIG. 11 is a graph showing densities in infiltrated regions in the
heat sink material shown in FIG. 9;
FIG. 12 is a graph showing densities in infiltrated regions in the
heat sink material shown in FIG. 9;
FIG. 13 is a graph showing densities in infiltrated regions in the
heat sink material shown in FIG. 9;
FIG. 14 is a table showing characteristics of heat sink materials
manufactured by the second manufacturing process;
FIG. 15 is a table showing characteristics of heat sink materials
manufactured by the second manufacturing process;
FIG. 16 is a table showing characteristics of heat sink materials
manufactured by the second manufacturing process;
FIG. 17 is a table showing characteristics of heat sink materials
manufactured by the second manufacturing process;
FIG. 18 is a graph showing porosities and densities of heat sink
materials manufactured by the second manufacturing process;
FIG. 19 is a graph showing densities and coefficients of thermal
conductivity of heat sink materials manufactured by the second
manufacturing process;
FIG. 20 is a table showing porosities and densities of heat sink
materials manufactured by the second manufacturing process;
FIG. 21 is a table showing porosities and densities achieved when
infiltrating pressures are changed in heat sink materials
manufactured by the second manufacturing process;
FIG. 22 is a perspective view showing a structure of a heat sink
material according to a second embodiment of the present
invention;
FIG. 23 is a cross-sectional view of a preforming machine for use
in a third manufacturing process;
FIG. 24 is a cross-sectional view of a hot press for use in the
third manufacturing process;
FIG. 25 is a flowchart of the third manufacturing process;
FIG. 26 is a flowchart of a fourth manufacturing process;
FIG. 27 is a cross-sectional view of a hot press for use in the
fourth manufacturing process;
FIG. 28 is a perspective view showing a structure of a heat sink
material according to a third embodiment of the present
invention;
FIG. 29 is a flowchart of a fifth manufacturing process;
FIG. 30 is a flowchart of a sixth manufacturing process;
FIG. 31 is a cross-sectional view showing a case with a powder
placed therein in a seventh manufacturing process;
FIG. 32 is a cross-sectional view showing the case with a lid
placed on the powder in the case in the seventh manufacturing
process;
FIG. 33 is a cross-sectional view showing the case with a molten
metal poured therein and depressed by a punch the seventh
manufacturing process;
FIG. 34 is a flowchart of the seventh manufacturing process;
FIG. 35 is a cross-sectional view of a hot press for use in an
eighth manufacturing process;
FIG. 36 is a flowchart of a manufacturing process according to a
fourth embodiment of the present invention;
FIG. 37A is a plan view of a packing;
FIG. 37B is a cross-sectional view taken along line
XXXVIIB--XXXVIIB of FIG. 37A;
FIG. 38 is a cross-sectional view of another hot press for use in
the eighth manufacturing process;
FIG. 39 is a cross-sectional view of a hot press for use in a
modification of the eighth manufacturing process;
FIG. 40 is a flowchart of the modification of the eighth
manufacturing process;
FIG. 41 is a cross-sectional view of a hot press for use in a ninth
manufacturing process; and
FIG. 42 is a flowchart of the ninth manufacturing process.
DETAILED DESCRIPTION OF THE INVENTION
As shown in FIG. 1, a heat sink material 10A according to a first
embodiment of the present invention comprises a porous sintered
body 12 having a metal 14 infiltrated into a network which is
formed by sintering carbon or an allotrope thereof.
The carbon or an allotrope thereof should have a coefficient of
thermal conductivity of 150 W/mK or higher, preferably a
coefficient of thermal conductivity of 200 W/mK or higher (an
estimated value with no pores), more preferably a coefficient of
thermal conductivity of 250 W/mK or higher (an estimated value with
no pores), or much more preferably a coefficient of thermal
conductivity of 300 W/mK or higher (an estimated value with no
pores).
According to the first embodiment, the heat sink material 10A
comprises a porous sintered body 12 having copper infiltrated into
open pores thereof. The porous sintered body 12 is made of graphite
having a coefficient of thermal conductivity of 150 W/mK or higher.
The metal 14 which infiltrates into the porous sintered body 12
should preferably comprise a metal having a property of expansion
upon solidification or a metal having a property of inhibiting a
solidification shrinkage, and may be Bi or a metal selected from Pb
and graphite cast iron, or an alloy containing at least one of
these metals.
The porous sintered body 12 and the metal 14 have volume ratio in
the ranges from 50 vol. % to 90 vol. % and from 10 vol. % to 50
vol. %, respectively. The heat sink material 10A thus made up of
the porous sintered body 12 and the metal 14 has a coefficient of
thermal conductivity of 300 W/mK or higher either on the average in
the directions of three orthogonal axes or in the direction of any
one of the three orthogonal axes, and a residual porosity of 5% or
less.
The porous sintered body 12 should preferably have a porosity in
the range from 10 vol. % to 50 vol. %. If the porosity of the
porous sintered body 12 were smaller than 10 vol. %, then it would
not be possible to achieve a coefficient of thermal conductivity of
300 W/mK or higher (at room temperature) either on the average in
the directions of three orthogonal axes or in the direction of any
one of the three orthogonal axes. If the porosity of the porous
sintered body 12 exceeded 50 vol. %, then the mechanical strength
of the porous sintered body 12 would be lowered, failing to keep
the residual porosity at 5% or less.
The porous sintered body 12 should preferably have an average open
pore diameter (pore diameter) in the range from 0.1 .mu.m to 200
.mu.m. If the pore diameter were less than 0.1 .mu.m, then it would
be difficult to infiltrate the metal 14 into the open pores,
resulting in a reduction in the coefficient of thermal conductivity
of the heat sink material 10A. If the pore diameter were greater
than 200 .mu.m, then the mechanical strength of the porous sintered
body 12 would be lowered, failing to lower the coefficient of
thermal expansion of the heat sink material 10A.
The porous sintered body 12 should preferably have such a
distribution of average open pores (pore distribution) that open
pores having diameters in the range from 0.5 .mu.m to 50 .mu.m
constitute 90% or more of all the pores. If open pores having
diameters in the range from 0.5 .mu.m to 50 .mu.m did not
constitute 90% or more of all the pores, then the porous sintered
body 12 would have more open pores not infiltrated by the metal 14,
and the coefficient of thermal conductivity of the heat sink
material 10A would be reduced.
The heat sink material 10A made of the porous sintered body 12
infiltrated by the metal 14 should preferably have a closed
porosity of 5 vol. % or less. If the closed porosity were in excess
of 5 vol. %, then the coefficient of thermal conductivity of the
heat sink material 10A would possibly be reduced.
The porosity, pore diameter, and pore distribution were measured
using an automatic porosimeter (tradename: Autopore 9200)
manufactured by Shimadzu Corp.
In the heat sink material 10A, it is preferable to add to the
graphite an additive for lowering the closed porosity at the time
the graphite is sintered. The additive may be SiC and/or Si. The
additive is effective to reduce closed pores produced at the time
the graphite is sintered to increase the rate of infiltration of
the porous sintered body 12 with the metal 14.
At least one material selected from Te, Bi, Pb, Sn, Se, Sb, Li, Tl,
and Cd should preferably be added to the metal 14 which infiltrates
into the porous sintered body 12. The added material improves the
wettability of the interface between the porous sintered body 12
and the metal 14, allowing the metal 14 to enter easily into the
open pores in the porous sintered body 12.
At least one material selected from Nb, Cr, Zr, Be, V, Mo, Al, Ta,
Mn, Si, Fe, Co, Ni, Mg, Ca, W, Ti, B, and mish metal should
preferably be added to the metal 14 which infiltrates into the
porous sintered body 12. The added material increases the reaction
between the graphite and the metal 14, allowing the graphite and
the metal 14 to match and closely contact each other in the open
pores with ease, and reducing the closed porosity of the heat sink
material 10A.
Several processes for manufacturing the heat sink material 10A
according to the first embodiment will be described below with
reference to FIGS. 2A through 21.
First and second manufacturing processes for manufacturing the heat
sink material 10A have the sintering step of producing the porous
sintered body 12 which is a network formed by sintering graphite,
and the infiltrating step of infiltrating the metal 14 into the
porous sintered body 12.
The first manufacturing process is carried out using a
high-pressure vessel 30 shown in FIGS. 2A and 2B. The high-pressure
vessel 30 comprises a prismatic housing 32 having a pair of
parallel spaced side walls 34, 36 supporting respective rotatable
shafts 38 on their substantially central areas. The housing 32 can
be rotated in unison with the rotatable shafts 38 about their
axes.
The housing 32 houses therein a refractory casing 40 and a heater
42 for heating the refractory casing 40. The refractory casing 40
is of a prismatic shape having a hollow space 44 defined therein,
and includes a side wall having a vertical opening 46 defined
therein which communicates with the hollow space 44. The hollow
space 44 includes a space (hereinafter referred to as "first
chamber 44a") disposed on one side of the opening 46 for storing a
solid or molten mass of the metal 14 as an infiltrating
material.
The hollow space 44 includes another space (hereinafter referred to
as "second chamber 44b") disposed on the other side of the opening
46 for storing a plurality of porous ceramic sintered bodies 12 as
specimens to be infiltrated. The second chamber 44b houses therein
a support mechanism for supporting the porous ceramic sintered
bodies 12 in the second chamber 44b to prevent the porous ceramic
sintered bodies 12 from dropping when the second chamber 44b is
positioned above the first chamber 44a. The heater 42 has such a
structure as to protect itself against destruction under a high
pressure of 300 MPa.
To the high-pressure vessel 30, there are connected a suction pipe
48 for evacuating the high-pressure vessel 30, and a gas inlet pipe
50 and a gas outlet pipe 52 for introducing and discharging a gas
for applying a high pressure and a cooling gas.
The first manufacturing process using the high-pressure vessel 30
will be described below with reference to FIG. 3.
In step S1, a rod of graphite is formed, infiltrated by pitch (a
type of coal tar), and sintered with heat, thus producing a porous
sintered body 12 of graphite.
Specifically, a rod of graphite is formed by mixing a powder of
graphite with pitch, and extruding the mixture into a rod of
graphite having a diameter ranging from 100 to 600 mm and a length
of about 3000 mm, in an atmosphere at a temperature of about
150.degree. C. The rod of graphite thus produced contains many
pores and has a low coefficient of thermal conductivity.
The rod of graphite is then deaerated in a vacuum to reduce pores
therein, and infiltrated by pitch while in the vacuum. The rod of
graphite is sintered at about 1000.degree. C. and then infiltrated
by pitch. The above process is repeated three times.
In order to increase the coefficient of thermal conductivity of the
rod of graphite, the rod of graphite is heated in a furnace at
about 3000.degree. C. To prevent the rod of graphite from burning,
the furnace is covered with a powder of carbon, and the rod of
graphite itself is also covered with a powder of carbon.
Alternatively, the rod of graphite may be heated by directly
passing an electric current through the rod of graphite.
The porous sintered body 12 thus produced may preliminarily be
machined depending on the shape of a final product to be
achieved.
Thereafter, in step S2, the high-pressure vessel 30 is initialized
to turn the refractory casing 40 to bring the first chamber 44a
thereof into a lower position.
Then, a plurality of porous sintered bodies 12 thus produced and a
solid mass of the metal 14 are placed in the refractory casing 40
in step S3. Specifically, the solid mass of the metal 14 is set in
the first chamber 44a, and the porous sintered bodies 12 are set in
the second chamber 44b. At this time, it is preferable to have the
porous sintered bodies 12 preheated. To preheat the porous sintered
bodies 12, the porous sintered bodies 12 are housed in a carbon
case or covered with a heat insulating material and then preheated.
When the porous sintered bodies 12 have reached a predetermined
temperature, the porous sintered bodies 12 which are in the carbon
case or covered with the heat insulating material are set in the
second chamber 44b as described above.
Thereafter, the high-pressure vessel 30 (and the refractory casing
40) is sealed, and evacuated through the suction pipe 48 to develop
a negative pressure in the high-pressure vessel 30 in step S4.
Thereafter, the heater 42 is energized to melt the solid mass of
metal 14 in the first chamber 44a with heat in step S5. The mass of
metal 14 thus melted will hereinafter be referred to as "molten
metal 14".
When the molten metal 14 in the first chamber 44a has reached a
predetermined temperature, the high-pressure vessel 30 is turned
180.degree. in step S6. Since the first chamber 44a is brought into
an upper position, the molten metal 14 in the first chamber 44a
drops by gravity into the second chamber 44b in the lower position.
Therefore, the molten metal 14 is infiltrated into the porous
sintered bodies 12.
Then, an infiltrating gas is introduced through the gas inlet pipe
50 into the high-pressure vessel 30, pressurizing the high-pressure
vessel 30 in step S7. Under the pressure developed in the
high-pressure vessel 30, the open pores in the porous sintered
bodies 12 are infiltrated by the molten metal 14.
After the infiltrating process is finished, a cooling process is
immediately initiated. In the cooling process, the high-pressure
vessel 30 is turned 180.degree. in step S8. Since the first chamber
44a is brought into the lower position, the molten metal 14 in the
second chamber 44a drops by gravity back into the first chamber
44a.
Because a portion of the molten metal 14 has been trapped in the
open pores in the porous sintered bodies 12, the molten metal 14
falling into the first chamber 44a in the lower position is a
residual molten metal which has not infiltrated into the porous
sintered bodies 12. When the residual molten metal has dropped into
the first chamber 44a, the porous sintered bodies 12 which are
infiltrated by the molten metal 14 are left in the second chamber
44a.
Thereafter, the infiltrating gas in the high-pressure vessel 30 is
discharged through the gas outlet pipe 52, and simultaneously a
cooling gas is introduced through the gas inlet pipe 50 into the
high-pressure vessel 30 in step S9. As the infiltrating gas is
discharged and the cooling gas is introduced, the cooling gas is
circulated thoroughly in the high-pressure vessel 30, quickly
cooling the high-pressure vessel 30. When the high-pressure vessel
30 is quickly cooled, the molten metal 14 which has infiltrated
into the porous sintered bodies 12 is solidified into the solid
metal 14 and expanded in volume. Therefore, the metal 14 which has
infiltrated into the porous sintered bodies 12 is firmly retained
in the porous sintered bodies 12.
According to another cooling process, as indicated by the
dot-and-dash line in FIG. 3, after step S8, the high-pressure
vessel 30 or the porous sintered bodies 12 infiltrated by the metal
14 are delivered into a cooling zone, and brought into a chill
block disposed in the cooling zone in step S10.
When contacted by the chill block, the porous sintered bodies 12
are quickly cooled. In this cooling process, the porous sintered
bodies 12 may be cooled while a cooling gas is sprayed on the
porous sintered bodies 12 or the chill block is being cooled by
water. Particularly, it is preferable to cool the porous sintered
bodies 12 in view of a effect of dead head.
According to the above steps of the first manufacturing process,
the porous sintered body 12 of graphite can easily be infiltrated
by the metal 14. The rate of infiltration of the porous sintered
body 12 with the metal 14 is increased. The heat sink material 10A
thus has a coefficient of thermal conductivity of 300 W/mK or
higher either on the average in the directions of three orthogonal
axes or in the direction of any one of the three orthogonal axes,
and a residual porosity of 5% or less.
If the porous sintered body 12 is made of SiC as described later
on, then a heat sink material 10A can easily be produced which has
an open porosity of 5% or less in a temperature range from the room
temperature to 200.degree. C. and has a coefficient of thermal
conductivity of 300 W/mK or higher either on the average in the
directions of three orthogonal axes or in the direction of any one
of the three orthogonal axes.
When the heater 42 is energized to melt the metal 14 in the first
chamber 44a with heat in step S5, the temperature (heated
temperature) from which the process goes to step S6 should be
30.degree. C. to 250.degree. C. higher than the melting point of
the metal 14 and more preferably be 50.degree. C. to 200.degree. C.
higher than the melting point of the metal 14. At this time, it is
preferable to keep a vacuum of 0.133 Pa (1.times.10.sup.-3 Torr) or
lower in the high-pressure vessel 30.
In step S7, the pressure that is applied to the high-pressure
vessel 30 by introducing the infiltrating gas into the
high-pressure vessel 30 should be in the range from 0.98 MPa to 202
MPa, preferably from 4.9 MPa to 202 MPa, or more preferably from
9.8 MPa to 202 MPa.
This pressure should preferably higher for the purposes of
increasing the rate of infiltration and the cooling capability.
However, if the pressure were too high, then the graphite would
tend to be broken, and the cost of the facility capable of
withstanding the pressure would be high. Therefore, the pressure
should be selected in view of these considerations.
The pressure should be applied to the high-pressure vessel 30 for a
period of time ranging from 1 to 60 seconds, or preferably from 1
to 30 seconds.
The pores in the porous sintered body 12 should preferably have an
average diameter ranging from 0.1 .mu.m to 200 .mu.m and a porosity
ranging from 10 vol. % to 50 vol. %.
If the porous sintered body 12 is made of SiC, as described later
on, then 90% or more of all the pores in the porous sintered body
12 should preferably have an average diameter ranging from 5 .mu.m
to 50 .mu.m, and the porous sintered body 12 should preferably have
a porosity ranging from 20 vol. % to 70 vol. %.
In the cooling process, the porous sintered body 12 should be
cooled at a rate of -400.degree. C./hour or higher during a period
from the temperature at the time of infiltration to 800.degree. C.,
and preferably a rate of -800.degree. C./hour or higher.
In step S7, the pressure applied to the high-pressure vessel 30 is
a pressure required to fully infiltrate the metal 14 into the open
pores in the porous sintered body 12. If open pores not infiltrated
by the metal 14 remained in the porous sintered body 12, then the
thermal conductivity would be greatly impaired. Therefore, it is
necessary to apply a high pressure to the high-pressure vessel
30.
The pressure to be applied to the high-pressure vessel 30 can
roughly be estimated by the Washburn's equation, and needs to be
larger as the pore diameter is smaller. For example, if the pore
diameter is 0.1 .mu.m, then the pressure to be applied to the
high-pressure vessel 30 is 39.2 MPa, if the pore diameter is 1.0
.mu.m, then the pressure to be applied to the high-pressure vessel
30 is 3.92 MPa, and if the pore diameter is 10 .mu.m, then the
pressure to be applied to the high-pressure vessel 30 is 0.392 MPa.
Actually, however, a higher pressure needs to be applied to the
high-pressure vessel 30 because a material having an average pore
diameter of 0.1 .mu.m contains pores having diameters of 0.01 .mu.m
or less. Specifically, a pressure of 392 MPa needs to be applied to
the high-pressure vessel 30 for infiltrating pores having diameters
of 0.01 .mu.m or less with the metal 14.
Some modifications of the first manufacturing process will be
described below with reference to FIGS. 4 and 5.
According to a first modification, as shown in FIG. 4, graphite is
sintered into a porous sintered body 12 in step S101. The
high-pressure vessel 30 is initialized to turn the refractory
casing 40 to bring the first chamber 44a thereof into a lower
position in step S102.
Then, the porous sintered body 12 is set in the second chamber 44b,
and molten metal 14 is poured into the first chamber 44a in step
S103.
Thereafter, when the molten metal in the first chamber 44a has
reached a predetermined temperature, the high-pressure vessel 30 is
turned 180.degree. in step S104. The molten metal 14 in the first
chamber 44a drops by gravity into the second chamber 44b in the
lower position. Therefore, the porous sintered body 12 is
infiltrated by the molten metal 14.
Then, an infiltrating gas is introduced through the gas inlet pipe
50 into the high-pressure vessel 30, pressurizing the high-pressure
vessel 30 in step S105. Under the pressure developed in the
high-pressure vessel 30, the open pores in the porous sintered body
12 are infiltrated by the molten metal 14.
A second modification will be described below with reference to
FIG. 5. In an infiltrating process according to the second
modification, a partition plate (not shown) made of a porous
ceramic material is disposed centrally in the refractory casing 40
in the high-pressure vessel 30. The partition plate divides the
space in the refractory casing 40 into the first chamber 44a and
the second chamber 44b.
The partition plate should be made of a porous ceramic material
having a porosity ranging from 40 vol. % to 90 vol. % and a pore
diameter ranging from 0.5 mm to 3.0 mm, and preferably be made of a
porous ceramic material having a porosity ranging from 70 vol. % to
85 vol. % and a pore diameter ranging from 1.0 mm to 2.0 mm.
According to the second modification, as shown in FIG. 5, graphite
is sintered into a porous sintered body 12 in step S201. The
high-pressure vessel 30 is initialized to turn the refractory
casing 40 to bring the first chamber 44a thereof into a lower
position in step S202.
Then, the porous sintered body 12 and a solid mass of metal 14 are
placed in the refractory casing 40 in the high-pressure vessel 30.
Specifically, the solid mass of metal 14 is set in the second
chamber 44b in the upper position, and the porous sintered body 12
is set in the first chamber 44a in the lower position step
S203.
Thereafter, the high-pressure vessel 30 (and the refractory casing
40) is sealed, and evacuated through the suction pipe 48 to develop
a negative pressure in the high-pressure vessel 30 in step
S204.
Thereafter, the heater 42 is energized to melt the solid mass of
metal 14 in the second chamber 44b with heat in step S205. Then,
when the molten metal 14 has reached a predetermined temperature,
an infiltrating gas is introduced through the gas inlet pipe 50
into the high-pressure vessel 30, pressurizing the high-pressure
vessel 30 in step S206. Under the pressure developed in the
high-pressure vessel 30, the molten metal 14 in the second chamber
44b located in the upper position passes through the partition
plate, and infiltrates into open pores in the porous sintered body
12 in the first chamber 44b located in the lower position.
A second manufacturing process will be described below with
reference to FIGS. 6 through 8. The second manufacturing process
uses a furnace 60 (see FIG. 6) for sintering graphite into the
porous sintered body 12 and a press 62 (see FIG. 7) for
infiltrating the metal 14 into the porous sintered body 12.
As shown in FIG. 6, the furnace 60 serves to graphitize carbon and
has a space 72 for accommodating a case 70 therein and a heater 74
for heating the case 70 accommodated in the space 72. The case 70
is made of a material such as graphite, ceramics, cerapaper (a heat
insulating material of ceramics such as alumina or the like). The
case 70 accommodates graphite therein.
As shown in FIG. 7, the press 62 has a mold 82 having an upwardly
open cavity 80, and a punch 84 insertable into the cavity 80 for
pressing a content in the cavity 80.
The second manufacturing process using the furnace 60 and the press
62 will be described below with reference to FIGS. 6 through 8.
First, graphite is placed into the case 70, and the case 70 is put
into the furnace 60 in step 301. The atmosphere in the furnace 60
is heated to sinter the graphite into a porous sintered body 12 in
step S302.
In the sintering step, a current may be passed through the graphite
to heat the graphite to about 3000.degree. C. for thereby producing
the porous sintered body 12.
Thereafter, the porous sintered body 12 together with the case 70
is removed from the furnace 60, and then placed into the cavity 80
in the press 62 in step S303.
Then, a molten mass 86 of metal 14 is poured into the case 70 in
step S304, after which the punch 84 is inserted into the cavity 80
to press the molten metal 86 in the case 70 in step S305. When the
molten metal 86 is thus pressed by the punch 84, the open pores in
the porous sintered body 12 are infiltrated by the molten metal
86.
In the above second manufacturing process, the punch 84 should
press the molten metal 86 preferably under a pressure ranging from
1 MPa to 202 MPa (10 atmospheric pressures to 2000 atmospheric
pressures). As shown in FIG. 7, the bottoms of the case 70 and the
mold 82 have gas removal holes 88, 90 for removing a gas remaining
in the porous sintered body 12 or gaps removing a gas remaining in
the porous sintered body 12. When the punch 82 is pressed into the
cavity 80, a gas remaining in the porous sintered body 12 is
removed through the gas removal holes 88, 90, making it possible to
infiltrate the molten metal 86 smoothly into the open pores in the
porous sintered body 12.
According to the above steps of the second manufacturing process,
the porous sintered body 12 of graphite can easily be infiltrated
by the metal 14. The rate of infiltration of the porous sintered
body 12 with the metal 14 is increased. The heat sink material 10A
thus produced by the above steps of the second manufacturing
process has a coefficient of thermal conductivity of 300 W/mK or
higher either on the average in the directions of three orthogonal
axes or in the direction of any one of the three orthogonal axes,
and a residual porosity of 5% or less.
A furnace having a preheating capability may be used instead of the
furnace 60. The furnace having a preheating capability preheats the
porous sintered body 12 of precompressed powder or graphite. The
graphite (or SiC described later on) turned into a network by
preheating can easily be infiltrated by the metal 14. The graphite
should preferably be preheated to a temperature which is about the
same as the temperature of the molten metal 86. Specifically, if
the molten metal 86 has a temperature of 1200.degree. C., then the
graphite should preferably be preheated to a temperature ranging
from 1000.degree. C. to 1400.degree. C.
An experiment will be described below. In this experiment, one type
of carbon (graphite) was infiltrated by different metals and
different additive elements, and the effects of the additive
elements with respect to different densities, different
coefficients of thermal conductivity, different coefficients of
thermal expansion, and different porosities, after the
infiltration, of the heat sink material 10A at different
infiltrated locations were observed. The results of the experiment
are shown in FIGS. 9 through 21.
FIG. 9 is a cross-sectional view, taken along line IX--IX of FIG.
1, of the heat sink material 10A manufactured by the second
manufacturing process. The different densities of the heat sink
material 10A were measured at six divided infiltrated locations 10a
through 10f in the heat sink material 10A.
FIGS. 10 through 13 show densities of the heat sink material 10A at
the infiltrated locations 10a through 10f. The heat sink material
10A had six types (75Sb-25Cu, 70Sb-30Te, 60Sb-40Sn, 15Ni-85Bi,
85Sb-15Bi, 70Sb-1Zr-29Sn) produced by adding the above additive
elements, and three types of the heat sink material 10A (70Ni-30Si,
75Al-25Si, 50Sn-50Cu) other than the six types were produced
according to the conventional process. A material (NS3-21) was
graphite serving as the matrix of the heat sink material 10A. It
can be seen that almost no variations in the density of the heat
sink material 10 are produced by adding the additive elements to
the metal 14, suggesting that the infiltrated locations 10a through
10f were infiltrated by the same amount of metal 14 and had the
same porosity.
FIGS. 14 through 20 show different coefficients of thermal
conductivity, different coefficients of thermal expansion, and
different porosities after the infiltration, in the examples in the
above experiment and four types of the heat sink material 10A
(95Sb-5Cu, 95Sb-5Bi, 95Sb-5Sn, 95Sb-5Te).
The types of the heat sink material 10A which were infiltrated by
the additive elements Sb, Sn, Bi had densities and coefficients of
thermal conductivity which were not different from a conventional
heat sink material which were infiltrated by pure aluminum, pure
copper, and pure nickel. This is because the addition of the
additive elements improved the wettability at the interface between
the carbon and the metal 14, increasing close contact between the
carbon and the metal 14.
It has been confirmed that the porosities of all carbon types which
were infiltrated by the additive elements were lower than those
which were infiltrated by pure copper, pure copper alloy, and pure
aluminum. This is also because the addition of the additive
elements improved the wettability at the interface between the
carbon and the metal 14, increasing close contact between the
carbon and the metal 14.
In each of the above samples, the ratio of the coefficient of
thermal conductivity in the direction of the plane to the
coefficient of thermal conductivity in the direction of the
thickness is 1:5 or less, exhibiting properties nearly equal to
isotropic properties. Therefore, when each sample is to be used as
a heat sink, a practical advantage is offered because no
consideration is to be given to the direction in which to install
the heat sink.
FIG. 21 shows densities of different types of the heat sink
material 10A manufactured under a higher infiltrating pressure than
in the above experiment, and porosities, after the infiltration,
thereof. One of the types of the heat sink material 10A (95Sb-5Cu)
was manufactured by the first manufacturing process, and the other
type of the heat sink material 10A (4.5Si-95.5 Cu) was manufactured
by the conventional process.
It can be seen from FIG. 20 that the types of the heat sink
material 10A manufactured under the increased infiltrating pressure
had residual porosities lower than those of the samples shown in
FIG. 20. However, a comparison between the density of the heat sink
material 10A manufactured by the first manufacturing process and
the densities of the types of the heat sink material 10A
manufactured under the lower infiltrating pressure shown in FIGS.
10 through 20 indicates that the increase in the infiltrating
pressure does not essentially affect the density and the residual
porosity after the infiltration. Rather, it is to be noted as shown
in FIG. 21 that a large reduction in the residual porosity is
achieved by changing infiltrating metals. Stated otherwise, an
effect produced by changing infiltrating metals is more significant
than an effect produced by increasing the infiltrating pressure.
Therefore, the heat sink material 10A infiltrated by additive
elements has a desired porosity and density even if it is
manufactured under a low infiltrating pressure.
A heat sink material 10B according to a second embodiment of the
present invention will be described below with reference to FIG.
22.
As shown in FIG. 22, the heat sink material 10B according to the
second embodiment is produced by mixing a powder 12a of carbon or
an allotrope thereof with a powder 14a of metal 14, and forming the
mixture at a predetermined temperature under a predetermined
pressure.
The carbon or an allotrope thereof should have a coefficient of
thermal conductivity of 150 W/mK or higher, preferably a
coefficient of thermal conductivity of 200 W/mK or higher (an
estimated value with no pores), more preferably a coefficient of
thermal conductivity of 250 W/mK or higher (an estimated value with
no pores), or much more preferably a coefficient of thermal
conductivity of 300 W/mK or higher (an estimated value with no
pores). In the second embodiment, diamond may be used instead of
graphite as the carbon. In the second embodiment, a powder of
graphite having a coefficient of thermal conductivity of 100 W/mK
or higher and a powder of copper are mixed with each other, and the
mixture is formed into the heat sink material 10B. The metal 14
should preferably comprise a metal having a property of expansion
upon solidification or a metal having a property of inhibiting a
solidification shrinkage, and may be Bi or a metal selected from
Sb, Ga and graphite cast iron, or an alloy containing at least one
of these metals.
Alternatively, the heat sink material 10B according to the second
embodiment may be manufactured by mixing a crushed and torn
material of carbon or an allotrope thereof (e.g., a crushed and
torn material of carbon fiber) and a powder 14a of metal 14 with
each other, and forming the mixture at a predetermined temperature
under a predetermined pressure.
The predetermined temperature should preferably be 10.degree. C. to
50.degree. C. lower than the melting point of the metal 14 in view
of the forming process in a press, and the predetermined pressure
should preferably be in the range from 10.13 MPa to 101.32 MPa (100
atmospheric pressures to 1000 atmospheric pressures).
The powder 12a of carbon or an allotrope thereof and the powder 14a
of the metal 14 should preferably have an average powder particle
size ranging from 1 .mu.m to 500 .mu.m. The volume ratio of the
carbon or an allotrope thereof ranges from 20 vol. % to 80 vol. %,
and the volume ratio of the metal 14 ranges from 80 vol. % to 20
vol. %. The heat sink material 10B thus manufactured has a
coefficient of thermal conductivity of 300 W/mK or higher either on
the average in the directions of three orthogonal axes or in the
direction of any one of the three orthogonal axes, and a residual
porosity of 5% or less.
In the heat sink material 10A according to the second embodiment,
an additive for making it possible to resinter the formed mixture
should preferably be added to the carbon or an allotrope thereof.
The additive may be SiC and/or Si. The addition of the additive
allows the formed mixture to be resintered at a temperature equal
to or higher than the melting point of the metal 14. Since
particles produced after the mixture is formed are joined together
by the resintering step, almost all grain boundary which would
impair the thermal conductivity can be eliminated, increasing the
thermal conductivity of the heat sink material 10B.
An additive element for reacting with the carbon or an allotrope
thereof may be added to the powder 12a of carbon or an allotrope
thereof. The additive element may be at least one material selected
from Ti, W, Mo, Nb, Cr, V, Zr, Be, Al, Ta, Mn, Si, Fe, Co, Ni, Mg,
Ca, B, and mish metal. The added additive element produces a
reaction layer (carbide layer) on the surface of the carbon or an
allotrope thereof when the mixture is formed or resintered,
increasing the bonding strength between the particles on the
surface of the heat sink material 10B.
The metal 14 should preferably comprise a metal having a property
of expansion upon solidification or a metal having a property of
inhibiting a solidification shrinkage, and may be a metal selected
from Bi, Sb, Ga and graphite cast iron, or an alloy containing at
least one of these metals. The metal 14 thus selected improves the
wettability of the interface between the carbon or an allotrope
thereof and the metal 14, and suppresses a reduction in the
shrinkage caused when the metal 14 is cooled to the room
temperature, making it possible to reduce the porosity of the heat
sink material 10B.
It is also preferable to add, to the metal 14, at least one metal
having a low melting point selected from Nb, Zr, Cr, and Be which
forms a solid solution with copper only at a weight ratio of 0.5
wt. % or less. The addition of the above metal can increase the
bonding strength between the particles of the metal 14 when the
mixture is formed.
Several processes (third and fourth manufacturing processes) for
manufacturing the heat sink material 10B according to the second
embodiment will be described below with reference to FIGS. 23
through 27.
As shown in FIGS. 23 and 24, a third manufacturing process uses a
preforming machine 100 (see FIG. 23) and a hot press 102 (see FIG.
24).
As shown in FIG. 23, the preforming machine 100 has a mold 112
having an upwardly open cavity 110, and a punch 114 insertable into
the cavity 110 for pressing a content in the cavity 110. A case 70
to be placed in the cavity 110 accommodates therein a mixture 104
of a powder 12a of carbon or an allotrope thereof with a powder 14a
of metal 14.
As shown in FIG. 24, the hot press 102 comprises a tubular housing
120, a lower punch 122 disposed in the housing 120 and serving as a
base, an upwardly open refractory casing 124 of graphite disposed
in the housing 120 and fixedly mounted on the lower punch 122, an
upper punch 126 disposed above the refractory casing 124 in the
housing 120 and movable into and out of the refractory casing 124,
and a heater 128 disposed in the housing 120 for heating the
refractory casing 124. The refractory casing 124 accommodates
therein a preformed body 106 of the mixture 104 which has been
formed by the preforming machine 100. The hot press 102 has a
suction pipe 130 for evacuating the housing 120.
The lower punch 122 has a passage 132 defined therein for passing
therethrough a heating fluid for heating the refractory casing 124
and a cooling fluid for cooling the refractory casing 124.
The third manufacturing process has a succession of steps to be
carried out as shown in FIG. 25. A powder 12a of carbon or an
allotrope thereof with a powder 14a of metal 14 are placed in the
case 70, and mixed to obtain a mixture 104 in step S401. Then, the
case 70 with the mixture 104 contained therein is put into the
cavity 110 in the mold 112 of the preforming machine 100 in step
S402. Thereafter, the punch 114 is pressed into the cavity 110,
preforming the mixture 104 into a preformed body 106 in step
S403.
Then, the preformed body 106 is removed from the mold 112, and
placed in the refractory casing 124 in the hot press 102 in step
S404. After the refractory casing 124 is sealed, the refractory
casing 124 is evacuated through the suction pipe 130, developing a
negative pressure therein in step S405. Thereafter, the heater 128
is energized to increase the temperature in the refractory casing
124 to a temperature which is 10.degree. C. to 50.degree. C. lower
than the melting point of the metal 14 in step S406.
When the temperature in the refractory casing 124 has reached the
desired temperature, the upper punch 126 is lowered to press the
preformed body 106 into the heat sink material 10B in step S407.
Thereafter, the heat sink material 10B is machined for use as an
actual heat sink material 10B. If an element for increasing the
bonding strength between the carbon or an allotrope thereof and the
metal 14 is added, then the heat sink material 10B produced after
the preformed body 106 is pressed may be heated to a temperature
equal to or higher than the melting point of the metal 14.
Preferred additive elements to be added to the carbon or an
allotrope thereof and preferred additive elements to be added to
the metal 14 have been described above, and will be described in
detail below.
The heat sink material 10B manufactured by the above steps of the
third manufacturing process has a coefficient of thermal
conductivity of 300 W/mK or higher either on the average in the
directions of three orthogonal axes or in the direction of any one
of the three orthogonal axes, and a residual porosity of 5% or
less.
A fourth manufacturing process will be described below with
reference to FIGS. 26 and 27. According to the fourth manufacturing
process, the preforming machine 100 shown in FIG. 23 is not used,
but only a hot press 102 shown in FIG. 27 is used.
As shown in FIGS. 26 and 27, a powder 12a of carbon or an allotrope
thereof with a powder 14a of metal 14 are placed in the case 70,
and mixed to obtain a mixture 104 in step S501. Then, the case 70
with the mixture 104 contained therein is directly put into the
refractory casing 124 in the hot press 102 in step S502. After the
refractory casing 124 is sealed, the refractory casing 124 is
evacuated through the suction pipe 130, developing a negative
pressure therein in step S503. Thereafter, the heater 128 is
energized to increase the temperature in the refractory casing 124
to a temperature which is 10.degree. C. to 50.degree. C. lower than
the melting point of the metal 14 in step S504.
When the temperature in the refractory casing 124 has reached the
desired temperature, the upper punch 126 is lowered to press the
mixture 104 into the heat sink material 10B in step S505.
The heat sink material 10B produced by the fourth manufacturing
process has a coefficient of thermal conductivity of 300 W/mK or
higher either on the average in the directions of three orthogonal
axes or in the direction of any one of the three orthogonal axes,
and a residual porosity of 5% or less.
A heat sink material 10C according to a third embodiment of the
present invention will be described below with reference to FIG.
28.
As shown in FIG. 28, the heat sink material 10C according to the
third embodiment is produced by pressing a mixture of a powder 12b
of carbon or an allotrope thereof and a binder into a preformed
body and then a block which may be shaped as a cube, a rectangular
parallelepiped, or any other shape, and then infiltrating a metal
14 into the block. The powder 12b may be the same as the powder 12a
of carbon or an allotrope thereof according to the second
embodiment. The heat sink material 10C may be formed into any shape
close to a final shape.
The carbon or an allotrope thereof may comprise graphite or
diamond. The metal 14 may comprise Bi or a metal selected from Sb,
Ga and graphite cast iron, or an alloy containing at least one of
these metals.
The powder 12b of carbon or an allotrope thereof should preferably
have an average powder particle size ranging from 1 .mu.m to 500
.mu.m. The average ratio of minimum and maximum lengths of the
particles of the powder 12b should preferably be 1:5 or less
between a direction in which said particle has said minimum length
and a direction in which said particle has said maximum length.
Though the heat sink material 10C thus constructed has no strong
network therein, it can be formed into any shape close to a final
shape. Therefore, any subsequent machining step for the heat sink
material 10C may be dispensed with. The volume ratio of the carbon
or an allotrope thereof ranges from 20 vol. % to 80 vol. %, and the
volume ratio of the metal 14 ranges from 80 vol. % to 20 vol.
%.
An additive element for reacting with the carbon or an allotrope
thereof may be added to the powder 12b of carbon or an allotrope
thereof. The additive element may be selected in the same manner as
with the second embodiment.
Various additive elements should preferably be added to the metal
14, as with the first embodiment. Those additive elements include
additive elements for improving wettability, additive elements for
increasing the reactivity between the carbon or an allotrope
thereof and the metal 14, and additive elements for lowering the
melting point.
A fifth manufacturing process for manufacturing the heat sink
material 10C according to the third embodiment will be described
below with reference to FIG. 29. According to the fifth
manufacturing process, a mixture is prepared by mixing a powder 12b
of carbon or an allotrope thereof with water or a binder in step
S601.
The mixture is then pressed into a preformed body (not shown) under
a predetermined pressure in step S602. The mixture may be pressed
by the press 62 (see FIG. 7) or the preforming machine 100 (see
FIG. 23).
Then, the preformed body is preheated to facilitate the
infiltration thereof with the molten metal 14 in step S603. If the
molten metal 14 has a temperature of about 1200.degree. C., then
the graphite should preferably be preheated to a temperature
ranging from 1000.degree. C. to 1400.degree. C. With the preheating
step, the binder used in step S601 may be dispensed with.
In step S604, the preformed body is sintered into a block by the
same sintering process as with the first embodiment.
The block is then infiltrated by the molten metal in step S605. The
block may be infiltrated by the same sintering process as with the
first embodiment. For example, the high-pressure vessel 30 (see
FIG. 2) may be used, and steps S2 through S9 of the first
manufacturing process (see FIG. 3) may be carried out to produce
the heat sink material 10C.
According to the fifth manufacturing process, the coefficient of
thermal expansion and the coefficient of thermal conductivity may
be controlled at desired values depending on the compression of the
powders in the pressing process in step S602.
The produced heat sink material 10C has its thermal conductivity
made more isotropic and has its wettability and material yield
increased.
Since a network is produced by the metal 14, the residual pores in
the heat sink material 10C are reduced.
The heat sink material 10C can be manufactured inexpensively.
Specifically, the block before it is infiltrated cannot be machined
as it is too brittle. However, since the preformed body can be
infiltrated after it is formed into a final shape, and can
withstand subsequent forces tending to cause certain plastic
deformations, the heat sink material 10C which may be complex in
shape can be manufactured inexpensively.
In the fifth manufacturing process, as with the various previous
manufacturing processes, an element for forming a carbide may be
added to the metal 14 to lower the coefficient of thermal
expansion, and an element for improving the wettability may be
added to increase the rate of infiltration.
A higher infiltrating pressure is effective to increase the rate of
infiltration, the mechanical strength, and the coefficient of
thermal conductivity.
A sixth manufacturing process for manufacturing the heat sink
material 10C according to the third embodiment will be described
below with reference to FIG. 30. According to the sixth
manufacturing process, a molten metal or a metal in a solid-liquid
phase (solid-liquid phase metal) is prepared in step S701. The
solid-liquid phase metal is a metal (generally, an alloy) which is
melted into a partly molten state or a molten metal which is cooled
and stirred into a partly solidified state, and refers to both a
metal directly heated into a partly molten state and a metal fully
melted and then cooled into a partly solidified state.
A power 12b of carbon or an allotrope thereof is mixed with the
molten metal 14 or the solid-liquid phase metal in step S702.
The molten metal 14 or the solid-liquid phase metal with which the
powder 12b is mixed is then cast, and the cast product is formed
into the heat sink material 10C in step S073.
The heat sink material 10C produced according to the sixth
manufacturing process has the same features as those of the heat
sink material produced according to the fifth manufacturing
process.
A seventh manufacturing process for manufacturing the heat sink
material 10 will be described below with reference to FIGS. 31
through 34.
According to the seventh manufacturing process, as shown in FIG.
31, a powder 12b of carbon or an allotrope thereof is placed in a
case 70 made of graphite, ceramics, or cerapaper, or as shown in
FIG. 32, a plate-like lid 92 of carbon (which has holes 94 defined
therein or which is porous for allowing a molten metal to pass
therethrough) is put on the powder 12b to prevent the powder 12b
from rising. Then, the case 70 with the powder 12b contained
therein is preheated and then infiltrated by metal.
Specifically, as shown in FIG. 31, the powder 12b is placed in the
case 70 in step S801 shown in FIG. 34. Then, as shown in FIG. 32,
the lid 92 is placed on the powder 12b in the case 70, and the case
70 is preheated in step S802. Thereafter, as shown in FIG. 33, the
case 70 with the powder 12b contained therein is placed into the
cavity 80 in the press 62, and the molten metal 86 such as copper
or the like is poured into the case 70 through the holes 94 in the
lid 92 in step S803. The case 70 may be heated without the lid 92,
or the molten metal 86 may be poured into the case 70 without the
lid 92.
As shown in FIG. 33, the punch 84 is inserted into the cavity 80
with the lid 92 in the case 70, depressing the molten metal 86 in
the case 70 into the powder 12b. Therefore, the power 12b is
infiltrated by the molten metal 86.
The heat sink material 10C produced according to the seventh
manufacturing process has the same features as those of the heat
sink material produced according to the fifth manufacturing
process.
An embodiment in which the porous sintered body 12 is made of SiC
will be described below. If SiC is used in the first embodiment
(the first manufacturing process, the first modification, the
second modification, and the second manufacturing process), then
the process of sintering graphite into the porous sintered body 12
(steps S1, S101, S201, S301, and S302) is not required, and the
heat sink material can be manufactured in the same process as with
the subsequent steps.
A manufacturing process (eighth manufacturing process) according to
the fourth embodiment in which the porous sintered body 12 is made
of SiC will be described below with reference to FIGS. 35 through
38.
As shown in FIG. 35, the eighth manufacturing process is carried
out using a hot press 1060. The hot press 1060 is structurally
identical to the hot press 102 described above with respect to the
second embodiment.
The hot press 1060 comprises a tubular housing 1062, a lower punch
1064 disposed in the housing 1062 and serving as a base, an
upwardly open refractory casing 1066 of graphite disposed in the
housing 1062 and fixedly mounted on the lower punch 1064, an upper
punch 1068 disposed above the refractory casing 1066 in the housing
1062 and movable into and out of the refractory casing 1066, and a
heater 1070 disposed in the housing 1062 for heating the refractory
casing 1066. The hot press 1060 has a suction pipe 1072 for
evacuating the housing 1062.
The refractory casing 1066 is of a tubular shape having a hollow
space 1074 therein. The upper punch 1068 has a flange 1076 on its
side wall for determining the stroke thereof. A packing 1078 is
attached to the lower surface of the flange 1076 for contacting the
upper end surface of the refractory casing 1066 to sealingly close
the refractory casing 1066. The lower punch 1064 has a passage 1080
defined therein for passing therethrough a heating fluid for
heating the space 1074 in the refractory casing 1066 and a cooling
fluid for cooling the space 1074 in the refractory casing 1066.
The eighth manufacturing process is carried out in successive steps
shown in FIG. 36.
Bodies of SiC 1020, a filter 1054 of porous ceramic material, and
masses of the metal 14, which are arranged successively upwardly in
the order named, are charged into the space 1074 in the refractory
casing 1066 in step S1301. The porous ceramic material of the
filter 1054 should preferably have a porosity ranging from 40% to
90% and pore diameters ranging from 0.5 mm to 3.0 mm, and more
preferably have a porosity ranging from 70% to 85% and pore
diameters ranging from 1.0 mm to 2.0 mm.
The filter 1054 functions as a partition plate separating the
bodies of the SiC 1020 and the masses of the metal 14 from each
other to keep them out of contact with each other. The portion of
the space 1074 in which the masses of the metal 14 are set above
the filter 1054 is defined as an upper chamber 1074a, and the
portion of the space 1074 in which the bodies of the SiC 1020 are
set beneath the filter 1054 is defined as a lower chamber
1074b.
After the refractory casing 1066 is sealed, the refractory casing
1066 is evacuated through the suction pipe 1072 to develop a
negative pressure in the chambers 1074a, 1074b in the refractory
casing 1066 in step S1302.
Then, the heater 1070 is energized to heat the masses of the metal
14 in the upper chamber 1074a into a molten state in step S1303. At
the same time that the heater 1070 is energized, the heating fluid
may be passed through the passage 1080 in the lower punch 1064 to
heat the space 1074 in the refractory casing 1066.
When the molten metal 14 in the upper chamber 1074a reaches a
predetermined temperature, the upper punch 1068 is moved downwardly
to pressurize the upper chamber 1074a to a predetermined pressure
in step S1304. At this time, the packing 1078 mounted on the flange
1076 of the upper punch 1068 and the upper end surface of the
refractory casing 1066 are held and pressed against each other,
sealing the refractory casing 1066 to prevent the molten metal 14
from leaking out of the refractory casing 1066.
The molten metal 14 in the upper chamber 1074a under the
predetermined pressure is pushed through the filter 1054 into the
lower chamber 1074b under the pressure in the upper chamber 1074a,
and is infiltrated into the SiC 1020 placed in the lower chamber
1074b.
When an endpoint preset by a given time management plan is reached,
i.e., when the infiltration of the SiC 20 with the molten metal 14
is saturated, the cooling fluid is passed through the passage 1080
in the lower punch 1064 to cool the refractory casing 1066
progressively upwardly, thus solidifying the molten metal 14
infiltrated into the SiC 1020 in step S1305. Until the
solidification of the molten metal 14 is completed, the space 1074
in the refractory casing 1066 remains pressurized by the upper
punch 1068 and the lower punch 1064.
When the solidification of the molten metal 14 is completed, the
SiC 1020 infiltrated by the metal 14 is removed from the refractory
casing 1066 in step S1306.
In the above eighth manufacturing process, the SiC 1020 and the
metal 14 are heated while being sufficiently deaerated, and after
the metal 14 is melted, it is quickly brought into contact with the
SiC 1020, and the SiC 1020 and the molten metal 14 are pressurized
and continuously held under pressure until the cooling process is
completed. Therefore, the SiC 1020 can efficiently be infiltrated
by the metal 14. While the SiC 1020 is infiltrated by the molten
metal 14 under a negative pressure in the above embodiment, the SiC
1020 may be infiltrated by the molten metal 14 under the normal
pressure.
As described above, after the molten metal 14 and the SiC 1020 are
pressurized, they are brought into contact with each other to
infiltrate the molten metal 14 into the SiC 1020. Therefore, any
reduction in the pressure at the time the molten metal 14 and the
SiC 1020 are brought into contact with each other is minimized, and
the molten metal 14 and the SiC 1020 are well kept under pressure
when the SiC 1020 is infiltrated by the molten metal 14.
In the above embodiment, the packing 1078 is mounted on the lower
surface of the flange 1076 on the upper punch 1068 in order to
prevent the molten metal 14 from leaking out of the refractory
casing 1066. However, as indicated by the two-dot-and-dash lines in
FIG. 35, the packing 1078 may be mounted on the upper end surface
of the refractory casing 1066. Alternatively, as shown in FIGS. 37A
and 37B, a packing assembly 1102 comprising two annular split
packings 1100 may be mounted on the lower end of the upper punch
1068, as shown in FIG. 38. When the molten metal 14 enters a space
1104 in the packing assembly 1102, each of the split packings 1100
is spread radially outwardly against the refractory casing 1066,
thus sealing the upper chamber 1074a to prevent the molten metal 14
from leaking out of the refractory casing 1066.
A modification of the eighth manufacturing process will be
described below with reference to FIGS. 30 and 40. Those parts in
FIG. 39 which are identical to those shown in FIG. 35 are denoted
by identical reference characters, and will not be described in
detail below.
The modification of the eighth manufacturing process employs a hot
press furnace 1060 shown in FIG. 39. The hot press furnace 1060
includes a filter 1110 of porous ceramic material fixedly
positioned vertically centrally in the space 1074 in the refractory
casing 1066, and a door 1112 openably and closably disposed in a
side wall of the lower chamber 1074b. The portion of the space 1074
which extends above the filter 1110 serves as the upper chamber
1074a, and the portion of the space 1074 which extends beneath the
filter 1110 serves as the lower chamber 1074b. The door 1112
disposed in the side wall of the lower chamber 1074b is of such a
structure that when the door 1112 is closed, it seals the lower
chamber 1074b.
The modification of the eighth manufacturing process is carried out
in successive steps shown in FIG. 40.
The masses of the metal 14 are charged into the upper chamber 1074a
in the refractory casing 1066, and the door 1112 is opened and the
bodies of the SiC 1020 are charged into the lower chamber 1074b in
step S1401.
Then, the door 1112 is closed to seal the lower chamber 1074b, and
the hot press furnace 1060 is sealed. Thereafter, the refractory
casing 1066 is evacuated through the suction pipe 1072, developing
a negative pressure in the chambers 1074a, 1074b in the refractory
casing 1066 in step S1402.
Then, the heater 1070 is energized to heat the masses of the metal
14 in the upper chamber 1074a into a molten state in step S1403. At
the same time that the heater 1070 is energized, the heating fluid
may be passed through the passage 1080 in the lower punch 1064 to
heat the space 1074 in the refractory casing 1066.
When the molten metal 14 in the upper chamber 1074a reaches a
predetermined temperature, the upper punch 1068 is moved downwardly
to pressurize the upper chamber 1074a to a predetermined pressure
in step S1404.
The molten metal 14 in the upper chamber 1074a under the
predetermined pressure is pushed through the filter 1110 into the
lower chamber 1074b under the pressure in the upper chamber 1074a,
and infiltrates into the SIC 1020 placed in the lower chamber
1074b.
When an endpoint preset by a given time management plan is reached,
the cooling fluid is passed through the passage 1080 in the lower
punch 1064 to cool the refractory casing 1066 progressively
upwardly, thus solidifying the molten metal 14 infiltrated into the
SiC 1020 in step S1405.
When the solidification of the molten metal 14 is completed, the
SiC 1020 infiltrated by the metal 14 is removed from the refractory
casing 1066 in step S1406.
The above modified manufacturing process can efficiently infiltrate
the molten metal 14 into the SiC 1020 as is the case with the
eighth manufacturing process. According to the modified process,
after the molten metal 14 and the SiC 1020 are pressurized, they
are brought into contact with each other to infiltrate the molten
metal 14 into the SiC 1020. Therefore, any reduction in the
pressure at the time the molten metal 14 and the SiC 1020 are
brought into contact with each other is minimized, and the molten
metal 14 and the SiC 1020 are well kept under pressure when the SiC
1020 is infiltrated by the molten metal 14. While the SiC 1020 is
infiltrated by the molten metal 14 under a negative pressure in the
above modification, the SIC 1020 may be infiltrated by the molten
metal 14 under the normal pressure.
A manufacturing process (ninth manufacturing process) according to
the fifth embodiment in which the porous sintered body 12 is made
of SiC will be described below with reference to FIGS. 41, 42.
Those parts in FIG. 41 which are identical to those shown in FIG.
35 are denoted by identical reference characters, and will not be
described in detail below.
The ninth manufacturing process is essentially the same in
principle as the manufacturing process according to the fourth
embodiment, but differs therefrom in that in the infiltrating
process, the SiC 1020 and the metal 14 are brought into contact
with each other under a negative pressure or normal pressure, and
then heated to melt the. metal 14.
Specifically, as shown in FIG. 35, the filter 1054 is not charged,
but bodies of the SiC 1020 and masses of the metal 14, which are
arranged successively upwardly in the order named, are charged into
the refractory casing 1066 of the hot press furnace 1060 which is
used in the eighth manufacturing process according to the third
embodiment.
The ninth manufacturing process according to the fifth embodiment
is carried out in successive steps shown in FIG. 42.
Bodies of the SiC 1020 and masses of the metal 14, which are
arranged successively upwardly in the order named, are charged into
the space 74 in the refractory casing 66 in step S1501.
After the hot press furnace 1060 is sealed, the refractory casing
1066 is evacuated through the suction pipe 1072 to develop a
negative pressure in the refractory casing 1066 in step S1502.
Then, the heater 1070 is energized to heat the masses of the metal
14 in the upper chamber 1074a into a molten state in step S1503. At
the same time that the heater 1070 is energized, the heating fluid
may be passed through the passage 1080 in the lower punch 1064 to
heat the space 1074 in the refractory casing 1066.
When the molten metal 14 in the refractory casing 1066 reaches a
predetermined temperature, the upper punch 1068 is moved downwardly
to pressurize the refractory casing 1066 to a predetermined
pressure in step S1504.
The molten metal 14 under the predetermined pressure is forced to
infiltrate into the SiC 1020 under the pressure in the refractory
casing 1066.
When an endpoint preset by a given time management plan is reached,
i.e., when the infiltration of the SiC 1020 with the molten metal
14 is saturated, the cooling fluid is passed through the passage
1080 in the lower punch 1064 to cool the refractory casing 1066
progressively upwardly, thus solidifying the molten metal 14
infiltrated into the SiC 1020 in step S1505. Until the
solidification of the molten metal 14 is completed, the space 1074
in the refractory casing 1066 remains pressurized by the upper
punch 1068 and the lower punch 1064.
When the solidification of the molten metal 14 is completed, the
SiC 1020 infiltrated by the metal 14 is removed from the refractory
casing 1066 in step S1506.
In the ninth manufacturing process, the SiC 1020 and the metal 14
are heated while being sufficiently deaerated, and after the metal
14 is melted while the metal 14 and the SiC 1020 are being held in
contact with each other, the space 1074 in the refractory casing
1066 is pressurized and continuously held under pressure until the
cooling process is completed. Therefore, the SiC 1020 can
efficiently be infiltrated by the metal 14.
The heat sink material according to the present invention has
characteristics balanced against the coefficient of thermal
expansion and the coefficient of thermal conductivity of actual
electronic parts (including semiconductor devices), and also has a
small porosity. The heat sink material thus has a high mechanical
strength and is of high quality.
Although certain preferred embodiments of the present invention
have been shown and described in detail, it should be understood
that various changes and modifications may be made therein without
departing from the scope of the appended claims.
* * * * *